The endothelial isoform of nitric oxide synthase (eNOS) is a key determinant of vascular homeostasis and endothelial cell metabolism. eNOS catalysis involves several redox-active cofactors, and NO itself can interact with reactive oxygen species. The bioavailability of endothelium-derived NO is impaired in vascular disease states associated with, increased oxidative stress. We hypothesize that redox regulation ofthe eNOS pathway represents a critical determinant of NO- and ROS-dependent signaling and metabolic regulation in vascular endothelial cells. The proposed studies have important points of intersection with experimental plans proposed by other Projects in this Program. eNOS catalysis involves several redox-active cofactors; changes in intracellular redox state affect the concentrations of these key cofactors, and lead to alterations in eNOS-modulated responses. The formation of cellular NO adducts is influenced by reactive nitrogen and reactive oxygen species and by the cellular thiol redox state. Phosphorylation of eNOS by the AMP-activated protein kinase (AMPK) is influenced by reactive oxygen species, providing an important link between oxidative stress, eNOS signaling, and endothelial cell metabolism. Statins also activate AMPK and modulate endothelial ROS production. eNOSJs targeted to signal-transducing membrane microdomains termed caveolae, where the enzyme interacts with the scaffolding/signaling protein caveolin-1. We discovered that siRNA-mediated knockdown of caveolin leads to a striking increase in ROS production from endothelial cells, and found that caveolin-1-/- mice show dramatic increases in oxidative stress. eNOS-caveolin interactions are modulated by statins, yet the roles of statins in modulation of redox pathways involving eNOS remain incompletely understood. Experiments proposed in Specific Aim 1 will identify the mechanisms whereby altered biopterin and thiol metabolism affects eNOS post-translational modifications, subcellular targeting, and ROS generation. Experiments in Specific Aim 2 will determine the mechanisms whereby caveolin, statins, and reactive oxygen species modulate AMP-activated protein kinase (AMPK) signaling to eNOS.